import com.sun.xml.internal.ws.util.StringUtils;

public class demo01 {

    public static void main(String[] args) {
        String str="";
        System.out.println(str);

        System.out.println(str.isEmpty());


        System.out.println(str==null);

        System.out.println(str=="");

        System.out.println(str.length());

        System.out.println("".equals(str));



        


        String str2=null;
        System.out.println(str2);

   //     System.out.println(str2.isEmpty());          //空指针


        System.out.println(str2==null);

        System.out.println(str2=="");

     //   System.out.println(str2.length());              //空指针

        System.out.println("".equals(str2));
    }
}
